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Re: [ftpext] Discouraging use of TCP "urgent data"

Fernando Gont <fernando@gont.com.ar> Wed, 22 September 2010 13:59 UTC

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Date: Wed, 22 Sep 2010 10:32:28 -0300
From: Fernando Gont <fernando@gont.com.ar>
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To: "William F. Maton" <wmaton@ottix.net>
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Cc: Alexey Melnikov <alexey.melnikov@isode.com>, ftpext@ietf.org
Subject: Re: [ftpext] Discouraging use of TCP "urgent data"
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Hi, William,

>> This is somewhat related to FTP: there is currently a document in IESG
>> review talking about deprecation (or strong discouragement) of use of
>> TCP urgent data:
>>
>> <https://datatracker.ietf.org/doc/draft-ietf-tcpm-urgent-data/>
>>
>> I would like to ask people to review this and tell me how this affect
>> FTP.
> 
> Just taking a quick peek, looks like it isn't relevant to RFC 4217 at
> least, but as section 14 points out, 'FTP uses the Telnet Interrupt
> Process and Data Mark commands in conjunction with Urgent data to
> preface two commands: ABOR (Abort Transfer) and STAT (Status request).'
> 
> If 'urgent data' isn't recommended for new apps, then FTP is ...... ?

FTP can get away with its use of urgent data because it's a legacy app
;-) . However, it should set SO_OOBINLINE (or the like) such that the
urgent data is delivered inline.

Please note that Cisco Pix (and probably others) clear the URG bit by
default.... so be prepared for the urgent indications to be unreliable...

Thanks!

Kind regards,
-- 
Fernando Gont
e-mail: fernando@gont.com.ar || fgont@acm.org
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1

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